Ice making machines, or ice makers, that employ freeze plates which comprise lattice-type cube molds and have gravity water flow and ice harvest are well known and in extensive use. Such machines have received wide acceptance and are particularly desirable for commercial installations such as restaurants, bars, motels and various beverage retailers having a high and continuous demand for fresh ice.
In these ice makers, water is supplied at the top of a freeze plate which directs the water in a tortuous path toward a water pump. A portion of the supplied water collects on the freeze plate, freezes into ice and is identified as sufficiently frozen by suitable means whereupon the freeze plate is defrosted such that the ice is slightly melted and discharged therefrom into a bin. Typically, these ice machines can be classified according to the type of ice they make. One such type is a grid style ice maker which makes generally square ice cubes that form within individual grids of the freeze plate which then form into a continuous sheet of ice cubes as the thickness of the ice increases beyond that of the freeze plate. After harvesting, the sheet of ice cubes will break into individual cubes as they fall into the bin. Another type of ice maker is an individual ice cube maker which makes generally square ice cubes that form within individual grids of the freeze plate which do not form into a continuous sheet of ice cubes. Therefore, upon harvest individual ice cubes fall from the freeze plate and into the bin. A controller controls the operation of the ice maker to ensure a constant supply of ice.
The cooling cycle of typical ice makers is comprised of two sub-cycles, the sensible cooling cycle and the latent cooling cycle. During the sensible cooling cycle the supplied water is continuously recirculated across the freeze plate and back to the water pump thereby cooling the supplied water. Once the supplied water reaches the freezing point the supplied water begins to freeze in the freeze plate, the latent cooling cycle begins and the amount of water falling from the freeze plate back to the water pump decreases slightly as ice is formed on the freeze plates.
Traditionally, the principal components of a refrigeration system for use in an ice maker include a refrigerant flowing serially through a compressor, a condenser, a thermal expansion valve, and an evaporator. The evaporator is thermally coupled to the freeze plate in order to freeze the supplied water into ice. However, the refrigeration load at any given point during the sensible cooling cycle is driven by water temperature and the refrigeration load at any given point during the latent cooling cycle is driven primarily by the thickness of the layer of ice on the freeze plate. As the water temperature drops during the sensible cooling cycle and as the thickness of the ice on the freeze plate increases through the latent cooling cycle, the corresponding refrigeration load on the ice maker decreases through the cooling cycle.